The present invention relates to alkaline earth alkylaryl sulfonates, their application as detergent/dispersant additives for lubricating oils, and methods for preparing those sulfonates.
In prior art, methods are known for preparing weakly or strongly superalkalinized sulfonates from sulfonic acids obtained by the sulfonation of different alkyl aryl hydrocarbons and from an excess of alkaline earth base.
The alkyl aryl hydrocarbons subjected to the sulfonation reaction are obtained by alkylation via the Friedel and Craft reaction of different aryl hydrocarbons, particularly aromatic, with two different types of olefin:
Branched olefins obtained by the oligo-polymerization of propylene to C15 to C42 hydrocarbons, particularly the propylene tetrapolymer dimerized to a C24 olefin, and
Linear olefins obtained by the oligo-polymerization of ethylene to C14 to C40 hydrocarbons.
It is easy to obtain a good dispersion in the medium of the alkaline earth base not fixed in the form of salt if the sulfonic acid is derived from a hydrocarbon obtained by alkylation of an aryl hydrocarbon with a branched olefin. It is difficult if the alkylation is effected with a linear olefin. It is particularly difficult for the alkylation of an aryl hydrocarbon where a high percentage of the alkylaryl hydrocarbon has the aryl substituent on positions 1 or 2 of the linear alkyl chain, due to the formation of a skin in the open air.
This poor dispersion is especially pronounced if the medium also contains a high proportion of sulfonate, that is if it corresponds to a low Base Number (between 3 and 60), hence to a low content of free lime and the absence of carbon dioxide and carbonate.
In fact, during the alkylation reaction with benzene or another aromatic or aryl hydrocarbon, 25 mole % of the alkylaryl hydrocarbon has the aryl substituent on positions 1 or 2 of the linear alkyl chain. Traditionally, aromatics attached at the 2-position of the alkyl group give the most absorption of water.
In the alkylation reaction of aromatics using normal alpha olefins (NAO), there are three competing reactions. They are (1) isomerization of the NAO, (2) alkylation of the aromatic with the olefin, and (3) dimerization of the olefin.
When prepared by the method described, for example in French Patent No. 2,564,830, this high proportion of alkyl aryl hydrocarbon having an aryl radical on position 1 or 2 of the linear alkyl chain results in a sulfonate that exhibits hygroscopic properties such that a superficial xe2x80x98skinxe2x80x99 is formed. This xe2x80x98skinxe2x80x99 makes this product unacceptable as an additive for lubricating oil.
Furthermore, the formation of this superficial skin is generally accompanied by a very low filtration rate, a high viscosity, a low incorporation of calcium, a deterioration of anti-rust performance, and an undesirable turbid appearance, or even sedimentation, when the sulfonate thus prepared is added at the rate of 10% by weight to a standard lubricating oil and stored for examination.
The Applicant has carried out chromatographic analysis to identify each of the different isomers differing by the position of the aryl radical on the carbon atom of the linear alkyl chain, and examined their respective influence on the properties of the corresponding alkyl aryl sulfonates of alkaline earth metals obtained from these different isomers.
The Applicant has thus discovered that he could overcome the aforementioned drawbacks, inasmuch as the mole % of the aryl hydrocarbon, other than benzene, having the aryl substituent on positions 1 or 2 of the linear alkyl chain was between 0 and 13%, and preferably between 5 and 11%, and more particularly between 7 and 10%.
This discovery was the subject of a French Patent Application filed Mar. 8, 1995 under No. 95 02,709 by the Applicant.
Yet the Applicant had not succeeded in obtaining satisfactory results when the aryl hydrocarbon was benzene, because, heretofore, he had never been able to prevent the formation of the skin with the use of this aromatic hydrocarbon, even if the hydrocarbon was alkylated with a very long chain linear mono olefin so that the mole % of the aryl hydrocarbon having the aryl substituent on positions 1 or 2 of the linear alkyl chain was between 0 and 13%, and preferably between 5 and 11%, and more particularly between 7 and 10%.
As a result of more intensive studies, the Applicant had discovered that the aforementioned drawbacks could be overcome by using a mixture of alkyl aryl sulfonates of superalkalinized alkaline earth metals comprising:
(a) from 50% to 85% of a linear mono-alkyl phenyl sulfonate in which the linear alkyl chain contains between 14 and 40 carbon atoms, and between 0 and 13 mole % of the phenyl sulfonate radical of the alkaline earth metal is fixed on position 1 or 2 of the linear alkyl chain, and
(b) from 15% to 50% of a heavy alkyl aryl sulfonate selected from:
(i) dialkyl aryl sulfonates wherein both alkyl substituents are linear alkyl chains, of which the sum of the carbon atoms is from 16 to 40, or
(ii) mono or polyalkyl aryl sulfonates wherein the alkyl substituent or substituents are branched chains, wherein the sum of the carbon atoms is from 15 to 48 carbon atoms.
This mixture of alkyl aryl sulfonates has a maximum of 10 mole % of the phenyl sulfonate radical of the alkaline earth metal fixed on position 1 or 2 of the linear alkyl chain. This mixture has no skin formation after three days of storage in an open jar at room temperature. It has good calcium incorporation, a low viscosity, good solubility, and good performances.
This discovery was the subject of a French Patent Application filed Sep. 5, 1996 under No. 96 10,833 by the Applicant.
As a result of more intensive studies, the Applicant had discovered a mixture of alkyl phenyl sulfonates of alkaline earth metals having low color and no skin formation even after three days of storage in an open jar at room temperature. That mixture comprises:
(a) from 20% to 70% of a linear mono alkyl phenyl sulfonate in which the linear mono alkyl substituent contains from 14 to 40 carbon atoms and the mole % of the phenyl sulfonate radical fixed on position 1 or 2 of the linear alkyl chain is between 10% and 25%, and
(b) from 30% to 80% of a branched mono alkyl phenyl sulfonate in which the branched mono alkyl substituent contains from 14 to 18 carbon atoms.
This discovery was the subject of a European Patent Application filed Jul. 31, 1998 under No. 98 401968.9 by the Applicant.
The present invention provides a highly overbased alkaline earth alkylaryl sulfonate having improved compatibility and solubility, while having low color and no skin formation.
While we have found that a too high concentration of 1-aryl or 2-aryl linear alkylaryl sulfonate causes skin formation in sulfonates, we have found that the higher BN (at least 250 BN) sulfonates are less sensitive to 2-aryl content in the alkylate because the 2-aryl content is diluted by the salts. Therefore, if the BN is high enough (at least 250), and the aryl radical is not phenol, then the mole % of the aryl-sulfonate radical fixed on position 1 or 2 of the linear alkyl chain can be between 13% and 30% (preferably between 15% and 25%) without any skin forming. This high mole percentage of 2-aryl gives a sulfonate having good water absorption properties.
The alkyl chain of that alkaline earth alkylaryl sulfonate is a linear chain that contains between 14 and 40 carbon atoms, preferably from 20 to 24 carbon atoms.
Preferably, the alkaline earth alkylaryl sulfonate has a mono-alkylate content of at least 87% and an Iodine number of less than 1.0.
Preferably, the alkaline earth alkylaryl sulfonate is derived from a C4-C40 normal alpha olefin, more preferably from a C20-C24 normal alpha olefin.
This alkaline earth alkylaryl sulfonate is preferably derived from an alkylate formed by the reaction of benzene and normal alpha olefin in the presence of hydrogen fluoride, preferably in a one-stage reactor. Preferably, the alkylate is formed in the presence of methanol and xylene, but preferably in the absence of chlorine.
Preferably, the alkaline earth alkylaryl sulfonate is used as a detergent/dispersant additive for lubricating oils. A lubricating oil formulation would contain a major amount of a base oil of lubricating viscosity and a minor amount (preferably from 0.5 to 40%) of the alkaline earth alkylaryl sulfonate of the present invention. In addition, the lubricating oil formulation would typically contain from 0 to 20% of at least one ashless dispersant, from 0 to 5% of at least one zinc dithiophosphate, from 0 to 10% of at least one oxidation inhibitor, from 0 to 1% of at least one foam inhibitor; and from 0 to 20% of at least one viscosity index improver.
This lubricating oil composition can be made by blending a major amount of a base oil of lubricating viscosity and from 0.5 to 40% of a detergent comprising the alkaline earth alkylaryl sulfonate of the present invention, preferably with from 0 to 20% of at least one ashless dispersant, from 0 to 5% of at least one zinc dithiophosphate, from 0 to 10% of at least one oxidation inhibitor, from 0 to 1% of at least one foam inhibitor; and from 0 to 20% of at least one viscosity index improver.
A concentrate can be formed comprising from about 10% to 90% of a compatible organic liquid diluent and from about 0.5% to 90% of the alkaline earth alkylaryl sulfonate of the present invention.